CVE-2026-18691Hinoki check available

Internal credential exposure via authentication downgrade

Published Aug 11, 2026 · Updated Aug 11, 2026

Authentication downgrade in MongoDB Server allows man-in-the-middle attackers to recover the cluster's shared internal credential. During intra-cluster connection setup, a network party can influence the authentication mechanism selected between replica set members, causing the shared credential to be transmitted in a less-protected form. Network access to member-to-member traffic and use of a shared internal credential are required; recovery grants internal-superuser authentication to deployment nodes.

CVSS severity9.0
Critical
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
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Summary

What happened

Authentication downgrade in MongoDB Server allows man-in-the-middle attackers to recover the cluster's shared internal credential. During intra-cluster connection setup, a network party can influence the authentication mechanism selected between replica set members, causing the shared credential to be transmitted in a less-protected form. Network access to member-to-member traffic and use of a shared internal credential are required; recovery grants internal-superuser authentication to deployment nodes.

The record

CVE
CVE-2026-18691
Published
Aug 11, 2026
Updated
Aug 11, 2026
Vendor
MongoDB
Product
MongoDB Server
Classifications
CWE-757, T1557
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.0 <7.0.40
  2. Affected versionversion=8.0 <8.0.29
  3. Affected versionversion=8.3.0 <8.3.8

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

MongoDB · MongoDB Serverversion=7.0 <7.0.40; version=8.0 <8.0.29; version=8.3.0 <8.3.8

Published CVSS scores

8.8MongoDB, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.0MongoDB, Inc.CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-757Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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